package com.dfxs.sqlSession;

import com.dfxs.config.BoundSql;
import com.dfxs.pojo.Configuration;
import com.dfxs.pojo.MappedStatement;
import com.dfxs.utils.GenericTokenParser;
import com.dfxs.utils.ParameterMapping;
import com.dfxs.utils.ParameterMappingTokenHandler;

import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.util.ArrayList;
import java.util.List;

/**
 * @author zhangdongsheng
 * @version 1.0
 * @describe
 * @date 2020/9/26 9:38
 */
public class SimpleExecutor implements Executor{

    @Override
    public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception {
        //1.注册驱动，获取连接
        Connection connection = configuration.getDataSource().getConnection();

        //2.获取sql语句 : select * from user where id = #{id} and username = #{username}
        //转换sql语句： select * from user where id = ? and username = ? ，转换的过程中，还需要对#{}里面的值进行解析存储
        String sql = mappedStatement.getSql();
        BoundSql boundSql = getBoundSql(sql);

        // 3.获取预处理对象：preparedStatement
        PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());

        // 4. 设置参数
        //获取到了参数的全路径
        String paramterType = mappedStatement.getParamterType();
        Class<?> paramtertypeClass = getClassType(paramterType);

        //获取sql语句中的#{id}中的id名称通过Java类的域反射机制得到对应域的属性值,并传递给PreparedStatement对象
        List<ParameterMapping> parameterMappingList = boundSql.getParameterMappingList();
        for (int i = 0; i < parameterMappingList.size(); i++) {
            ParameterMapping parameterMapping = parameterMappingList.get(i);
            String content = parameterMapping.getContent();

            //反射
            Field declaredField = paramtertypeClass.getDeclaredField(content);
            //暴力访问
            declaredField.setAccessible(true);
            Object o = declaredField.get(params[0]);

            preparedStatement.setObject(i+1,o);
        }

        //5.执行SQl
        ResultSet resultSet = preparedStatement.executeQuery();
        String resultType = mappedStatement.getResultType();
        Class<?> resultTypeClass = getClassType(resultType);

        ArrayList<Object> objects = new ArrayList<>();
        //6.封装返回结果集
        while(resultSet.next()){
            Object o = resultTypeClass.newInstance();
            //元数据
            ResultSetMetaData metaData = resultSet.getMetaData();
            for (int i = 1; i <= metaData.getColumnCount(); i++) {
                //字段名
                String columnName = metaData.getColumnName(i);
                //字段的值
                Object value = resultSet.getObject(columnName);

                //使用反射或内省,根据数据库表和实体的对应关系,完成封装
                PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName, resultTypeClass);
                Method writeMethod = propertyDescriptor.getWriteMethod();
                writeMethod.invoke(o,value);
            }
            objects.add(o);
        }

        return (List<E>) objects;
    }

    private Class<?> getClassType(String paramterType) throws ClassNotFoundException {
        if (paramterType!=null){
            Class<?> aClass = Class.forName(paramterType);
            return aClass;
        }
        return null;
    }

    /**
     * 完成对#{}的解析工作：1.将#{}使用？进行代替，2.解析出#{}里面的值进行存储
     * @param sql
     * @return
     */
    private BoundSql getBoundSql(String sql) {
        //标记处理类：主要是配合通用标记解析器GenericTokenParser类完成对配置文件等的解 析工 作，其中TokenHandler主要完成处理
        ParameterMappingTokenHandler parameterMappingTokenHandler = new ParameterMappingTokenHandler();
        //GenericTokenParser :通用的标记解析器，完成了代码片段中的占位符的解析，然后再根 据 给定的标记处理器(TokenHandler)来进行表达式的处理
        //三个参数：分别为openToken (开始标记)、closeToken (结束标记)、handler (标记处 理器)
        GenericTokenParser genericTokenParser = new GenericTokenParser("#{", "}", parameterMappingTokenHandler);
        //获取解析后的sql语句
        String parseSql = genericTokenParser.parse(sql);
        //#{}里面解析出来的参数名称
        List<ParameterMapping> parameterMappings = parameterMappingTokenHandler.getParameterMappings();

        BoundSql boundSql = new BoundSql(parseSql,parameterMappings);
        return boundSql;
    }
}